Valve for controlling liquids

ABSTRACT

A valve ( 1 ) for regulating fluids has a piezoelectric unit ( 4 ) for actuating a valve member ( 3 ). The valve member is embodied with a control piston ( 9 ), adjacent to the piezoelectric unit ( 4 ), and with at least one actuating piston ( 14 ), adjacent to a valve closing member ( 15 ). A hydraulic chamber ( 16 ) functioning as a hydraulic booster is disposed between the pistons ( 9, 14 ). The valve closing member ( 15 ) cooperates with at least one valve seat ( 18, 19 ) and divides a low-pressure region ( 20 ) from a high-pressure region ( 21 ). An electric control unit ( 12 ) specifies the trigger voltage for the piezoelectric unit ( 4 ) as a function of the pressure level in the high-pressure region ( 21 ), a leakage loss from the low-pressure region ( 20 ) and the hydraulic chamber ( 16 ), and the refilling of the low-pressure region.

BACKGROUND OF THE INVENTION

The invention is based on a valve for regulating fluids.

One such valve is described, in German Patent Disclosure DE 197 328 02,for a fuel injection device of an internal combustion engine having ahigh-pressure system (common rail system). This fuel injection devicehas two valve seats, which cooperate with sealing faces of a valveclosing member upon actuation by a piezoelectric drive in a sequence ofmotion, in which the valve closing member is initially in the closingposition on the first valve seat, then is moved into an intermediateposition between the valve seats, and then returns to a closing positionagainst the second valve seat. To that end, a piezoelectric actuator ischarged to a rail-pressure-dependent voltage, which causes an elongationof the actuator and a resultant motion of the valve closing membertoward the second valve seat. For the reversing motion of the valveclosing member in the direction of the first valve seat, the actuator isdischarged again.

By the course of motion of the valve closing member from one valve seatto the other, a brief relief of a valve control chamber, which is underhigh pressure, is attained; by way of its pressure level, an opening andclosing position of a valve needle is determined in the fuel injectiondevice, which is embodied in force-balanced fashion, and the fuelinjection is thus controlled. The fuel injection is enabled while thevalve closing member is in an intermediate position between the twovalve seats. In this way, even a double fuel injection, such as apre-injection and a main injection, can be achieved by means of a singleexcitation of the piezoelectric drive.

Since the triggering of the valve member is done not directly but ratherby means of a hydraulic booster, the pressure buildup in the hydraulicchamber, functioning as a hydraulic coupler, is decisive for the lengthof the stroke of the valve member. If the piezoelectric actuator issubjected to such high voltage that the valve closing member moves outof its valve seat, then some of the fuel quantity located in thehydraulic chamber is forced out via the leakage gaps from this chamber.This effect is especially pronounced if the control valve is held on thesecond valve seat, toward the high-pressure region, since in that casethe counterpart force from the rail pressure is especially strong. Therefilling of the low-pressure region or of the hydraulic coupler is doneby means of a system pressure, which in practice can for instance amountto 15 bar, once again via these leakage gaps, but in this case onlyduring the time while the piezoelectric actuator is not triggered.

The same is true for similar valves known from practice, which areequipped with only one valve seat and in which the valve closing memberis lifted out of this valve seat and moved back again.

In all these valves, when injections occur in quick succession, theproblem exists that the hydraulic coupler is as a rule not completelyrefilled. The valve stroke that is set with the same trigger voltage ofthe piezoelectric actuator and thus the same actuator stroke in theseinjections therefore varies. The closer together two injections occur,that is, the shorter the refill time between injections is, and thelonger the actuator was previously triggered or in other words thegreater the loading time of the hydraulic coupler and thus the greaterthe leakage quantity, the more marked is the adverse effect described.The variable actuator stroke in turn disadvantageously causesinaccuracies in metering the injection quantity; under somecircumstances, the actuator stroke can be so short that it has no effecton the valve needle, and in the case involving use as a fuel injectionvalve, no fuel injection for instance occurs.

SUMMARY OF THE INVENTION

The valve of the invention for regulating fluids, has the advantage thatthe valve stroke that is set can be executed identically for allinjections, by means of a suitably modified trigger voltage of thepiezoelectric unit. It is thus possible, even at a high prevailingpressure level in the high-pressure region, to execute injections inquick succession, as may be necessary in a pre-injection, main injectionand post-injection to improve the fuel consumption and emissions values,with a replicable stroke length for all the injections, since thevarying fill level of the low-pressure region or of the hydrauliccoupler, which is represented by the hydraulic chamber, can becompensated for by way of the trigger voltage.

With the valve of the invention, in which in addition to taking thepressure level in the high-pressure region into account, a modificationof the trigger voltage is done as a function of leakage losses andrefilling, a stable injection can advantageously be guaranteed.

In an especially advantageous version of the invention, it can beprovided that to ascertain the leakage loss from the low-pressureregion, a triggering duration of a preceding injection is output to theelectric trigger unit. The triggering duration of the precedinginjection represents a reliable variable for the quantity of hydraulicfluid that was expelled through leakage points during the loading timeof the hydraulic coupler.

In a further advantageous version of the valve of the invention, it canprovided that a time interval between an end of the preceding injectionand the onset of the next injection is output to the electric controlunit as a highly reliable value for the refilling of the low-pressureregion, because this time interval as a rule does correspond to therefilling time. The fill factor of the coupler before the next injectioncan thus be determined from the refill time and the loading time.

Further advantages and advantageous features of the subject of theinvention can be learned from the specification, drawing and claims.

BRIEF DESCRIPTION OF THE DRAWING

One exemplary embodiment of the valve of the invention for regulatingfluids is shown in the drawing and will be described in further detailin the ensuing description. Shown are

FIG. 1, a schematic detail showing one exemplary embodiment of theinvention in a fuel injection valve for internal combustion engines inlongitudinal section; and

FIG. 2, a signal flow block diagram with a performance graph of anelectric control unit for correction of the trigger voltage of apiezoelectric unit of the fuel injection valve of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The exemplary embodiment shown in FIG. 1 illustrates a use of the valveof the invention in a fuel injection valve 1 for internal combustionengines of motor vehicles. The fuel injection valve 1 here is embodiedas a common rail injector, and the fuel injection is controlled via thepressure level in a valve control chamber 2, which communicates with ahigh-pressure supply means.

To adjust an injection onset, injection duration and injection quantityvia force ratios in the fuel injection valve 1, a valve member 3 istriggered via a piezoelectric unit, embodied with a piezoelectricactuator 4, which is disposed on the side of the valve member 3 towardthe valve control chamber and the combustion chamber.

The piezoelectric actuator 4 is constructed of multiple layers in aknown manner, and on its side toward the valve member 3 it has anactuator head 5, while on its side remote from the valve member 3 it hasan actuator foot 6, which is braced against a valve body 7. A controlpiston 9 of the valve member 3 is embodied with a stepped diameter andcontacts the actuator head 5 via a bearing plate 8.

To subject the piezoelectric actuator 4 to voltage, contacts 10, 11 areprovided on the actuator base 6; they are connected to an electriccontrol unit 12, shown only symbolically in FIG. 1, which triggers thepiezoelectric actuator 4. The valve member 3 that can be actuated viathe piezoelectric actuator 4 is disposed axially displaceably in a bore13 embodied as a longitudinal bore and is embodied in multiple parts;besides the control piston 9, it also has an actuating piston 14, whichis provided for actuation of a ball-shaped valve closing member 15. Thecontrol piston 9 and the actuating piston 14 are coupled to one anotherby means of a hydraulic booster.

The hydraulic booster, by means of which the deflection of thepiezoelectric actuator 4 is transmitted to the valve closing member 15,is represented by a hydraulic chamber 16. Between the two pistons 9 and14 defining this chamber, of which the actuating piston 14 is embodiedwith a smaller diameter than the control piston 9, the hydraulic chamber16 encloses a common compensation volume. Between the control piston 9and the actuating piston 14, the hydraulic chamber 16 is fastened insuch a way that the actuating piston 14 executes a stroke that islengthened by the boosting ratio of the piston diameter when the largercontrol piston 9 is moved by a certain distance by the piezoelectricactuator 4. The piezoelectric actuator 4, control piston 9 and actuatingpiston 14 are located one after the other on a common axis.

Besides providing hydraulic force transmission, the hydraulic chamber 16also serves as a tolerance compensation element for variations inlengthwise expansion in the components of the fuel injection valve 1caused by temperature gradients or different temperature expansioncoefficients of the materials used, as well as for possible settlingeffects. The pistons 9 and 14 can dip into the volume of the hydraulicchamber 13 and withdraw again without causing any change in the positionof the valve closing member 15 to be triggered.

The valve closing member 15 cooperates in a valve chamber 17 with twovalve seats 18, 19, embodied on the valve body 7, on the end of thevalve member 3 or actuating piston 14 toward the valve chamber. Thefirst or upper valve seat 18 defines a low-pressure region 20, while thesecond or lower valve seat 19 leads to the valve control chamber 2,which is associated with a high-pressure region 21. A spring 28 isassigned to the second valve seat 19 and keeps the valve closing member15 against the first valve seat 18 if the valve control chamber isrelieved.

A movable valve control piston, not otherwise shown in the drawing, isdisposed in the valve control chamber 2 of the high-pressure region 21.By axial motions of the valve control piston in the valve controlchamber 2, an injection nozzle of the fuel injection valve 1 iscontrolled in a manner known per se. Typically, an injection line whichsupplies the injection nozzle with fuel also discharges into the valvecontrol chamber 2. The injection line communicates with a high-pressurestorage chamber (common rail) that is common to a plurality of fuelinjection valves. The high-pressure storage chamber is supplied withfuel at high pressure from a tank in a known manner by a high-pressurefuel feed pump.

A valve system pressure chamber 22 adjoins the end of the bore 13 towardthe piezoelectric unit. This hydraulic pressure chamber is defined onone side by the valve body 7 and on the other by a sealing element 23,which is connected to the control piston 9 of the valve member 3 and tothe valve body 7, and which in this case is embodied as a bellowslikediaphragm and prevents the piezoelectric actuator 4 from coming intocontact with the fuel contained in the valve system pressure chamber 22.

Since during a pause in triggering or current supply to thepiezoelectric actuator 4 the hydraulic chamber 16 has to be refilledagain, provision is made for compensating for a leakage quantity fromthe low-pressure region 20 by withdrawal of hydraulic fluid from thehigh-pressure region 21. This purpose is served by a filling device 24,which discharges into the valve system pressure chamber 22 andcommunicates with the hydraulic chamber 16 via a gap 25, surrounding thecontrol piston 9, so that via the gap 25, filling of the hydraulicchamber 16 is also possible.

It is understand that in a version deviating from this, it may beprovided that the filling device 24 discharges into a differenthydraulic pressure chamber or directly into the gap 25 or into a gap 26that surrounds the actuating piston 14.

The fuel injection valve 1 of FIG. 1 functions as described below.

In the closed state of the fuel injection valve 1 and with thepiezoelectric actuator 4 uncharged, the valve closing member 15 of thevalve member 3 is kept in contact with the upper valve seat 18 assignedto it, so that no fuel from the valve control chamber 2 communicatingwith the high-pressure storage chamber can reach the low-pressure region20.

In the case of a slow actuation, as occurs in the event of atemperature-dictated change in length of the piezoelectric actuator 4 orother valve components, such as the valve body 7, the control piston 9as the temperature increases penetrates the compensation volume of thehydraulic chamber 16, or retreats from it again if the temperaturedrops, without this having any effects on the closing and openingposition of the valve member 3 and of the fuel injection valve 1.

If an injection by the fuel injection valve 1 is to take place, thepiezoelectric actuator 4 is supplied with current, and as a result itabruptly increases its axial length. Via the control piston 9 and thehydraulic chamber 16, this elongation of the piezoelectric actuator 4 istransmitted to the actuating piston 14, as a result of which the valveclosing member 15 is lifted out of the first, upper valve seat 18 andmoved toward the second, lower valve seat 19 counter to the prevailingrail pressure.

In setting the voltage exerted on the piezoelectric actuator 4, not onlythe pressure level in the high-pressure region 21, that is, the railpressure, but also the leakage loss on the low-pressure region 20 out ofthe hydraulic chamber 16 during a previous injection El and therefilling are taken into account by the electric control unit 12.

As FIG. 2 shows, the electric control unit 12 to this end has aperformance graph 27; as input data, a triggering duration T_E1 of thepreceding injection E1 and a time interval T_E1E2 between the end of thepreceding injection E1 and the onset of the next injection E2 are used.The triggering duration T_E1 of the preceding injection E1 and the timeinterval T_E1E2 indicate the leakage loss from the low-pressure region20 and the refilling time since the preceding injection E1,respectively. As a function of these input data, a correction value ofthe trigger voltage ΔU is output; this is added to the fundamental valueof the trigger voltage, which is dimensioned primarily on the basis ofthe rail pressure. The correction value ΔU of the trigger voltage isdimensioned such that the trigger voltage increases in successiveinjections, in order to compensate for a difference between the leakageloss and the refilling of the low-pressure region 20. In this way, areplicable stroke length of the valve member 3 or actuating piston 14 isattained, and it is assured that on the one hand a correct injectionoccurs, and on the other, the valve closing member 15 always achievescontact with the second valve seat 19.

The triggering of the piezoelectric unit becomes even more precise ifthe electric control unit 12 additionally corrects the trigger voltagewith regard to the current temperature of the piezoelectric actuator 4.

It is understood that it may also be provided that the valve closingmember 15 is stabilized in its middle position. Provision can also bemade that the valve 1 does not function as a bidirectional valve, butthan instead, the valve closing member cooperates only with the firstvalve seat 18. Triggering in which the valve closing member is moved athigh speed and high voltage into the second valve seat 19, so that theinjection takes place in the return motion from the second valve seat 19to the first valve seat 18, is also conceivable in the valve of theinvention.

It is understand that in a departure from the double-seat valve versionshown, a version of the fuel injection valve with only one seat is alsopossible.

What is claimed is:
 1. A valve for regulating fluids, having apiezoelectric unit (4) for actuating a valve member (3), which isaxially displaceable in a bore (13) of a valve body (7) and is embodiedwith at least one control piston (9), adjacent to the piezoelectric unit(4), and at least one actuating piston (14), adjacent to a valve closingmember (15), between which pistons a hydraulic chamber (16) acting as ahydraulic booster is disposed, and the valve closing member (15)cooperates with at least one valve seat (18, 19) for opening and closingthe valve and divides a low-pressure region (20) from a high-pressureregion (21), and the pressure level in the high-pressure region (21) isone parameter for setting a trigger voltage for the piezoelectric unit(4), characterized in that an electric control unit (12) specifies thetrigger voltage for the piezoelectric unit (4) as a function of aleakage loss from the low-pressure region (20), in particular from thehydraulic chamber (16), and of the refilling of the low-pressure region.2. The valve of claim 1, characterized in that to ascertain the leakageloss from the low-pressure region (20), a triggering duration (T_E1) ofa preceding injection (E1) is output to the electric trigger unit (12).3. The valve of claim 2, characterized in that the electric control unit(12) has a performance graph (27), by means of which a correction value(ΔU) for the trigger voltage is output as a function of the triggeringduration (T_E1) of the preceding injection (E1) and/or the time interval(T_E1E2) since the preceding injection (E1).
 4. The valve of claim 1,characterized in that to ascertain the refilling of the low-pressureregion (20), a time interval (T_E1E2) between an end of the precedinginjection (E1) and the onset of the next injection (E2) is output to theelectric control unit (12).
 5. The valve of claim 1, characterized inthat a temperature of the piezoelectric unit (4) is one parameter foradjusting the trigger voltage.
 6. The valve of claim 1, characterized inthat the trigger voltage in successive injections is increased such thata difference between the leakage loss and the refilling of thelow-pressure region (20) is compensated for, and the stroke of the valveclosing member (15) is constant.
 7. The valve of claim 1, characterizedin that for refilling the low-pressure region (20), a filling device(24) is provided, which can communicate with the high-pressure region(21) and has a system pressure chamber (22), which discharges into a gap(26) surrounding the actuating piston (14) or into a gap (25)surrounding the control piston (9).
 8. The valve of claim 1,characterized by its use as a component of a fuel injection valve forinternal combustion engines, in particular of a common rail injector(1).